Consumer sensing applications are often required to perform highly accurate measurements for a relatively short period of time relative to the total time the sensor is activated. High accuracy measurements are often achieved with analog circuitry having large bias currents that will dominate quiescent current consumption between MEASUREMENT phases. Consumer sensors with digital outputs offer a programmable data rate to provide the best trade-off between performance, (e.g. noise in particular) and current consumption.
A common use case includes configuring an accelerometer to operate at a low data rate to monitor motion in the application, with very low power consumption. When motion is detected, the microcontroller changes the configuration of the sensor to operate at a higher data rate to get a series of high accuracy, low noise measurements of the acceleration.
To offer a wide range of Output Data Rates (ODRs), consumer accelerometers employ pulsed operation. For example, low-noise signal acquisition and conversion is performed during a MEASUREMENT phase with relatively high current consumption (IDD). The MEASUREMENT phase has a fixed duration and repeats at a frequency equal to the ODR. Between two consecutive MEASUREMENT phases is an IDLE phase with the duration dependent on the ODR. The current consumption during the IDLE phase is reduced to the minimum to operate as a voltage regulator to supply power to the digital block of the accelerometer and to keep a user-programmed register content and a low-frequency oscillator operational to control the length of this IDLE phase.